If you belong to a credit union, call it as well. (Credit unions have made a specialty of car loans and offer lower-than-average rates. To find one you can join, visit the Credit Union National Association online.)

When you find what you think is the best rate for you, don't hesitate -- just go for it. There's very little downside.

But the one thing you don't want to do is extend the term of your loan. Most lenders will happily match the term on your loan, even if it's between their normal terms of 36, 48 and 60 months.

To figure your savings, just subtract your new monthly payment from your old one.